The invention relates in general to techniques for detecting substances immobilized to a substrate, and in particular to a method and apparatus employing a sensor array operated at AC frequencies.
With the advent of the human genome project and other gene sequencing technologies, techniques for performing sequencing has been of great interest. There are many other medical, biological and analytical applications for sensor arrays. One sequencing technique involves the detection of fluorescently labelled materials, such as that described in U.S. Pat. No. 5,143,854. Such devices typically include a microscope and a monochromatic or polychromatic light source for directing light at a substrate. A photon counter detects fluorescence from the substrate, while an x-y translation stage varies the location of the substrate. A computer controls the movement of the x-y translation table and data collection. Light from the light source is focused at a substrate surface by manually adjusting the microscope. Manual adjustment may be time consuming and inconvenient. Furthermore, due to the inherent imperfections present in the x-y translation table and substrate, the substrate may be out of focus when it is moved by the table so that the data collected may be inaccurate.
Other devices for detecting fluorescently labelled materials employ charge coupled devices instead of microscopes. While such devices avoid the need for many adjustments of the microscope, such devices have limited resolution. In some sensor units available commercially, each sensor unit typically has dimensions of 20 microns by 20 microns.
It is therefore desirable to provide an improved technique for detecting immobilized substances on a substrate where the above-described difficulties and limitations are avoided.